Molten iron is periodically tapped from the base of a blast furnace and flows along a trough or runner to a mold, ladle, or the like and the slag floating atop the metal is separated out by appropriately positioned baffles. Obviously the very hot--1300.degree. C. to 1500.degree. C.--molten metal and the slag are highly corrosive and hence erode the runner considerably.
At one time the furnace was tapped infrequently enough that the runner could be serviced between tappings, although the hot environment of the base of the blast furnace did not make such servicing convenient. Nowadays it is common to leave the runner at least partially full of molten iron between taps which may be 5h to 8h apart. Thus for servicing of this wear-prone runner it is necessary to shut down the furnace, a costly thing to do.
Accordingly the interior of the runner is lined with refractory material of a type similar to that used in metallurgical crucibles. This lining is fitted directly into the normally reinforced-concrete foundation of the blast furnace. Between tappings the temperature of the metal and slag in the runner still remains above 1300.degree. C. Thus considerable heat is transmitted through the tile lining to the foundation, creating substantial thermal stresses. Cracking and breakouts around the runner are common.
It has therefore been suggested to mount the refractory lining in a metal trough supported above the floor adjacent the blast furnace. Forced or natural air flow over the trough cools it to 150.degree. C. to 300.degree. C. Such cooling does not permit particular areas of the runner to be cooled more or less, depending on operation. In addition this system is subjected to considerable differential thermal expansion and contraction as regards the cool metallic trough and its hot refractory lining, so that cracking of same is common, in particular when the runner is completely emptied. Once the lining is cracked the hot iron can contact the sheet-metal trough and damage it.